I use a 4gb usb stick with aptosid.
In order to enable the persistent option I did so with the aptosid-to-usb script. Problem now is that I am unable to du because I would have to download more than 900 mb and that kind of free space is not available anymore.
Question now is:
At boot I have the option between 32 and 64bit. Obviously I don't really need both of them. So could I just rm a folder with the 32bit information in or is that not possible. If it is possible which files and folder would we talk about?
I know that I could always use the light.iso one and installing the rest, but I would rather not. If someone could advice me if there is an easy solution.

You can strip the iso before you put it onto your stick (fll-iso-strip). As long as you have enough space somewhere you could even do that now and replace the iso on the stick with the created smaller one.